Usually, firearm shotshell ammunition is manufactured by inserting an ignition primer into a cartridge. A measured or selected amount of propellant is inserted or poured into the cartridge. The propellant has a portion thereof contiguous with the primer. A wad, manufactured from a fixed size of material such as cardboard (“nitro card”), cork, plastic and the like, is inserted into the cartridge. One portion of the wadding thereof is contiguous with the propellant.
A projectile, slug or slugs, pellets, spheres, cubes, etc. in any geometric shape may be inserted into the cartridge. The projectile(s) may, if desired, be manufactured from lead, iron or other suitable material, including non-toxic material. The projectile(s) has one portion thereof contiguous with the wadding material. The cartridge is closed by pressure fitting a portion of the cartridge around the projectile(s). The pressure fitting may be accomplished by rolling or folding the cartridge mouth onto the projectile, then crimping the distal edge of the cartridge around the projectile(s). A six or eight point fold or “star” crimp may typically be used in cartridges that contain multiple projectiles (“shot”). An overshot card may be used with a roll crimp to contain shot loads. The loaded ammunition is ready to be packaged with other loaded ammunition.
Typically, ammunition is fired from a firearm by first placing the ammunition into the breach of the firearm. Examples of firearms are rifles, pistols, shotguns, muskets and military type weapons like artillery pieces. In firing the ammunition, a mechanical force is applied against the ignition primer causing an explosion. The resulting action ignites the propellant causing an expanding hot gas to propel the projectile(s) laterally along the bore of the firearm.
Practically, the firing sequence discussed above is ideal and the actual firing sequence includes the burning propellant gases, wadding, and projectile(s), entering a forcing cone before entering the bore of the firearm. The forcing cone is an area between the end of the cartridges in the breach and the bore of the firearm. The large end of the forcing cone is contiguous with the breach and the smaller end is contiguous with the bore. The forcing cone compresses the hot gas and wadding thereby increasing the force present on the projectile(s). If the wadding is not perfectly fitted in the cartridge hull, as well as fitting the chamber throat and forcing cone, the compressed hot gas may not obturate or seal the compressed hot gas. This results in a blow-by effect of the hot gas and possible loss of pressure and projectile speed, or balling of the shot, causing a decrease in the performance of the firearm. If the blow-by effect is sufficient, this may result in obstruction of the bore causing possible damage or rupture of the firearm when firing a second round of ammunition.
It would be desirable to have the full pressure of the compressed gas be developed and contained in the area of the hull, chamber and forcing cone without the blow-by effect. Further, it would be desirable to have a wadding system that does not require the wad to be manufactured or to be perfectly fitted in the cartridge or in the forcing cone.